Ice-Inspired Superlubricated Electrospun Nanofibrous Membrane for Preventing Tissue Adhesion.

Inspired by the superlubricated surface (SLS) of ice, which consists of an ultrathin and contiguous layer of surface-bound water, we built a SLS on the polycaprolactone (PCL)/poly(2-methacryloxyethylphosphorylcholine) (PMPC) composite nanofibrous membrane via electrospinning under controlled relative humidity (RH). The zwitterionic PMPC on the nanofiber provided a surface layer of bound water, thus generating a hydration lubrication surface. Prepared under 20% RH, electrospun PCL/PMPC nanofibers reached a minimum coefficient of friction (COF) of about 0.12 when the weight ratio of PMPC to PCL was 0.1. At a higher RH, a SLS with an ultralow COF of less than 0.05 was formed on the composite nanofibers. The high stability of the SLS hydration layer on the engineered nanofibrous membrane effectively inhibited fibroblast adhesion and markedly reduced tissue adhesion during tendon repair in vivo. This work demonstrates the great potential of this ice-inspired SLS approach in tissue adhesion-prevention applications.

Electrical friction modulation on MoS2 using electron beam radiation without electrostatic interactions.

Nanoscale friction under different electronic states and the corresponding friction controlling methods are both scientifically interesting and technologically important. However, friction measurements under electrical modulation are severely hampered by electrostatic forces induced by the charge-trapping effect. Therefore, in this study, we developed a new modulation method free from the charge-trapping effect through electron beam radiation; this method successfully modulated the friction between few-layer MoS2 and the silicon tip on atomic force microscopy. Friction on monolayer MoS2 increased under electron beam radiation. Strong correlations between the accelerating voltage, beam current, and friction force were found, and constant adhesion force demonstrate that the influence of static electricity was eliminated in this method. Excited electron states caused by electron injection could be possible mechanisms for friction modulation. However, the electron beam radiation had a negligible influence on the friction of bilayer MoS2. This study is the first of its kind, revealing the effect of electron beam radiation and electronic states on friction, which is important for the development of tribological theories and nanoelectromechanical systems, and offers a new electrical modulation method for friction tuning.

Dual functional electrospun core-shell nanofibers for anti-infective guided bone regeneration membranes.

In clinic infection is the paramount cause for failure of guided bone regeneration (GBR) membranes. Therefore, it is crucial to develop anti-infective GBR membranes for clinical bone repair application. In this research, we successfully prepared electrospun core-shell nanofibers loaded with metronidazole (MNA) and nano-hydroxyapatites (nHA), which could be employed for anti-infective GBR membranes due to the achievement of dual functions with enhanced osteogenesis and slow MNA release. The nanofiber shell was composed of polycaprolactone and nHA, whilst the nanofiber core was gelatin and MNA. The MNA release and cell proliferation experiments showed that compared with directly MNA-loaded nanofibers, the core-shell nanofibers possessed slower MNA release profile, which resulted in the decrease in cytotoxicity of MNA to bone mesenchymal stem cells. The osteogenic measurements demonstrated that the core-shell nanofibers could enhance bone formation. Additionally, the anti-bacterial experiments indicated that the core-shell nanofibers could prevent colonization of anaerobic bacteria. In summary, the results in the present study revealed the potential of the core-shell electrospun nanofibers with dual functions of enhanced osteogenesis and anti-infection for optimal clinical application as GBR membranes.

Differences in Tribological Behaviors upon Switching Fixed and Moving Materials of Tribo-pairs including Metal and Polymer.

The coefficient of friction (COF) between two materials is usually believed to be an intrinsic property of the materials themselves. In this study, metals of stainless steel (304) and brass (H62), and polymers of polypropylene (PP) and polytetrafluoroethylene (PTFE) were tested on a standard ball-on-three-plates test machine. Significantly different tribological behaviors were observed when fixed and moving materials of tribo-pairs (metal/polymer) were switched. As an example, under the same applied load and rotating speed, the COF (0.49) between a rotating PP ball and three fixed H62 plates was approximately 2.3 times higher than that between switched materials of tribo-pairs. Meanwhile, the COF between H62 and PTFE was relatively stable. The unexpected tribological behaviors were ascribed to the thermal and mechanical properties of tribo-pairs. Theoretical analysis revealed that the differences in the maximum local temperature between switching the fixed and moving materials of tribo-pairs were consistent with the differences in the tested COF. This result indicated the precise prediction of the COF of two materials is complexcity, and that thermal and mechanical properties should be properly considered in designing tribo-pairs, because these properties may significantly affect tribological performance.